A sun photometer is a device that measures amount and distribution of light coming from the sky. The sun photometer may estimate the state of the atmosphere through the information on measured amount and distribution of light. Herein, the light as an object of measurement may include lights by reflection, refraction, and scattering. For reference, they are together called “scattered lights” in this specification.
The state of the atmosphere may show characteristic patterns of atmospheric particles. The sun photometer may estimate characteristics of the atmospheric particles through light distribution patterns. For example, light reflecting characteristics may depend on characteristics of the atmospheric particles. The characteristics of particles may include particle sizes, particle shapes, transmittance, etc.
To determine the state of the atmosphere, a sun tracking method and a sky scanning method may be used.
The sun tracking is a method that measures amount and distribution of light, toward the sun. Information measured by the sun tracking includes atmospheric transmittance, aerosol optical depth, Angstrom exponent, aerosol extinction, moisture (H2O), ozone (O3), etc.
The sky scanning is a method of scanning the whole sky regardless of the sun. It may discretely scan the sky from different ranges of azimuthal angles. Herein, the angle toward the sun may be excluded. To scan the different ranges of azimuthal angles, a motor may rotate probes to a specific azimuthal angle. Information measured by the sky scanning includes scattering phase function, asymmetry parameter, aerosol size distributions, aerosol sphericity, aerosol absorption, cloud optical properties, etc.
One of measurement methods using the sun tracking and the sky scanning is a method by installing the sun photometer in an aircraft, etc. For example, when an aircraft on the ground measures a state of atmosphere such as a pattern of atmospheric scattering through ground observations, the state of all layers of the atmosphere may be measured. More specifically, if the distance from the surface of the earth to the sun is L, and if an aircraft at an altitude of ΔL measures a state of atmosphere through aerial observation, the state of all the layers of the atmosphere corresponding to a height of L′, where L′=L−ΔL may be measured. In addition, if the aircraft measures a state of the atmosphere corresponding to the height of L′ which varies as ΔL, the states of the atmosphere at each altitude may be found. The conventional photometer is shown in FIG. 1. By referring to FIG. 1, the photometer is illustrated on the top left and the state of the photometer being installed in an aircraft is illustrated.
However, the measurement method by using such an aircraft has a problem that it takes more time and errors in measurement occur as a position of the aircraft changes. Specifically, as the sky scanning may be operated by a motor, calibration is required due to changes in measuring angles depending on rotations of the motor and changes in measuring positions depending on movements of the aircraft. In other words, by referring to FIG. 1, the photometer shown on the top left may be rotated by a motor while installed in the aircraft. For example, if 100 seconds are required to scan the whole sky while the azimuthal angles are changed by using the motor, the aircraft may move a distance of roughly 10 kilometers for 100 seconds. Besides, even under the sun tracking, the photometer installed in the aircraft as shown in FIG. 1 could track the sun while being rotated by the motor. While angles of probes are changed by the motor to track a position of the sun, the aircraft could move a considerable distance and errors in measurement could occur.
Accordingly, the present inventor came to develop non-power driven technology that allows intensity of light to be measured by kinematically placing multiple probes that receive or detect lights entering from different ranges of individual azimuthal angles.